Controlling Reproductive Behavior in Performance Mares

Imagine this scenario: You are lucky enough to have the horse of your dreams. She's an athletic and beautiful mare, but there’s one problem--she's notorious for displaying "marish" behavior, and it's starting to get in the way of training and competition. What can be done? According to one researcher, there are several options to consider to dial down her undesirable reproductive behavior.

"Reversible suppression of sexual behavior in mares used for sporting purposes is frequently demanded to control undesirable behavior traits, particularly in mares that will be used for breeding in the future," explained Dominik Burger, Dr.med.vet, head of the Research and Reproduction Unit from the Swiss National Stud, in Avenches, Switzerland, at the 12th Congress of The World Equine Veterinary Association, held Nov. 2-6, 2011, in Hyderabad, India.

Burger noted this task must be broached delicately so that it is reversible and does not impart any lasting detrimental effects on fertility.

According to Burger, there are several options to help control untoward behavior in athletic mares. For example, veterinarians can administer either intramuscular exogenous progesterone or oral synthetic progestin (e.g., altrenogest) to maintain sufficient levels of circulating progesterone to prevent estrus and related behavior. However, not all equestrian federations allow this treatment.

"Two points worth considering are that long-term treatment with gestagens (such as Regumate) can increase the uterine susceptibility for inflammation and infection, and their short duration of action, necessitating repeated oral or intramuscular administration, make all progestin products costly and somewhat impractical," Burger pointed out.

Alternatively, Burger discussed the practice of inserting one to three glass balls measuring 30-35 mm in diameter into the mare's uterus to simulate a gestation, a practice that is also thought to help control untoward behavior.

"Glass balls are very well tolerated, rarely lost spontaneously, and are easily removed by manual manipulation per rectum," he noted.

Finally, Burger discussed a new vaccine that has been designed specifically for use in the mare: "One study documents the effect of this vaccine using a conventional two-dose immunization regime. All mares responded to vaccination for a minimum of three months. Although this vaccine has a high level of safety, some doubt persists about its long-term effect on a mare's reproductive potential after repeated use."

This vaccine works by introducing gonadotropin-releasing hormone (GnRH) antibodies, which inactivate the GnRH produced by the mare. Simply put, the whole hormonal cascade is temporarily interrupted and the ovaries are essentially deactivated.

The vaccine is currently registered in Australia, but is not yet available in North America.